Positron Emission Tomography (PET) is a procedure used for imaging and measuring physiologic processes within the human body. As part of the procedure, radioisotopes are injected into a patient to assist in diagnosing and assessing a disease. A cyclotron or particle accelerator is used to produce the radioisotopes. In a cyclotron, a particle beam is accelerated which then bombards a target material housed in a target system of the cyclotron. Referring to FIG. 1a, a general configuration for shielding a cyclotron 10 is shown. The cyclotron 10 is positioned between movable shields 12 and 14 (shown in an open position thus exposing the cyclotron 10) and stationary shields 16 and 18. Referring to FIG. 1b, the cyclotron 10 generates a particle beam 20 that then bombards target material 22 located within target enclosure 24 to produce a radioactive isotope which then decays. The decay of the isotope as well as other interactions generates gamma and neutron radiation 26 that is attenuated by the shields 12,14,16,18 so as to protect personnel in the vicinity of the cyclotron against unsafe levels of radiation.
Typically, cyclotron shields are configured as large, monolithic blocks of shielding material that includes lead shot suspended in a polymer matrix, for example. However, this approach has disadvantages from the viewpoint of design, manufacturing, disposal and the environment. In particular, it is preferable that the material used for the shields is specifically adapted for shielding against the radiation that is being emitted, such as gamma and neutron radiation, so that each form of radiation is addressed separately. Further, an approach to shielding is needed which is easily configured to better suit the needs of specific cyclotron configurations, uses materials which minimizes potential environmental effects and is easier to assemble during manufacturing and disassemble for appropriate disposal when decommissioning a shield.